The present invention relates to a technology for inspecting the track pitch of the magnetic disk in a magnetic disk drive.
Magnetic disk drives are information recording/reproducing devices that record/reproduce data by reading with a head the servo information written on a magnetic disk, and recognizing the position of the servo information. Typical methods of arranging servo information on a magnetic disk are the servo-surface servowriting scheme and the data-surface servowriting scheme (or the sector servowriting scheme). The servo-surface servowriting scheme is a scheme in which one side of one of plural disks is used exclusively for servo information. The data-surface servowriting scheme is a scheme for recording servo information intermittently in a circumferential direction between data regions on the recording surfaces of plural magnetic disks.
The methods of writing servo information on a magnetic disk can be broadly divided into two types: one type in which, after the magnetic disk has been built into a magnetic disk drive, servo information is written using the head of the magnetic disk drive, and the other type in which servo information is written on the magnetic disk with the disk separated from the magnetic disk drive. The former type includes a writing scheme, also referred to as the push-pin scheme, in which the magnetic disk drive is built into a servo track writer (STW) and then servo information is written using the head moved by the positioning pin of the STW. The former type also includes the so-called self-servowriting scheme. In this scheme, first servo information is written in a reference position previously set inside the magnetic disk drive, then next servo information is written with the position of the previous servo information used as a reference, and this procedure is repeated for each set of servo information to be written.
The latter type includes the so-called pre-servowriting scheme in which the magnetic disk is independently built into an STW and then servo information is written using the head of the STW. The latter type also includes the so-called stamping scheme in which the servo information pre-written on a master magnetic disk is written on other magnetic disks by means of magnetic transfer or the like. Since servo information is for positioning the head, the writing position of the information is required to be highly accurate.
In recent years, the margins between data tracks in magnetic disks have been decreasing with increases in the inter-track density (tracks per inch: TPI) of each disk. The margin between data tracks is a spacing between adjacent tracks, and refers to a region in which no data is written using a recording head. Increases in TPI lead to an increased risk of “squeezing”, the event that when the head records data on a data track, the data pre-recorded on adjacent tracks is magnetically affected to disturb recorded binary digit strings.
The head recognizes track positions with the position of servo information used as its reference. Therefore, if the servo information is written such that the pitch of adjacent servo information is smaller than a reference pitch, this is equivalent to the fact that the track pitch has become shorter than its original value, and thus results in squeezing. In short, a change in the pitch of the servo information is equivalent to a change in the track pitch. Changes in the pitch of servo information are due to the mechanical, thermal, and electrical changes occurring in devices related to the writing of the servo information. The changes in the pitch, therefore, are likely to occur in the above-described writing schemes such as the push-pin scheme, self-servowriting scheme, and pre-servowriting scheme. The changes in the pitch of the servo information also become a problem in the servo-surface servowriting scheme and the data-surface servowriting scheme.
The event in which the pitch of servo information changes is observed as an AC-like change in which the pitch regularly changes in plus and minus directions with respect to a reference pitch, or as a DC-like change in which the pitch changes from the reference pitch only by a required value in a certain range. In both cases, it is necessary to detect pitch changes during a product-shipping pre-inspection process and take the proper measures. Patent Document 1 (Japanese Patent Laid-open No. 7-153212) discloses a technology relating to a track width inspection device intended to detect a track width.